Printing plate preparation



Patented Oct. 6, 1942 I UNITED, STATES PATENT OFFICE ass-1.9::

rammcmmrmangnox I wm ge.xfii d o?z dford, Ohio, alllsnor to No Drawing.Application August 31, 1940, Serial No. 355,024

8Clalms.

Company, Cleveland,

plates such as afore-mentioned, with surfacing which presents,advantages over such substances as albumen, gum arabic, dextrine, etc.previously involved.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the water,leaving hardened albumen in those areas whichcorrespond to the image to be printed.

In the manufacture of so-called deep-etch" lithographic plates, alight-sensitized resist" is removed by development with water, leavinghardened coating as a protective resist over the non-image areas of theplate. An etching solu-' tion, as for instance iron chloride is thenemployed to eat away the unprotected image parts I of the plate to adesired depth. The etched parts are then filled with an ink receptivelacquer, ink is applied, and the hardened protective resist is removedby dilute citric acid solution leaving the plate clean in the unetchednon-image areas. In

the manufacture of half-tone relief plates and some forms of intaglioplates, while in many instances a shellac resist or cold top enamel isapplied and the plate is etched by nitric acid, it is also common tomake such plates by means of materials similar to those just mentionedfor deep etch lithographic plates, viz. gum arabic.

and dextrine resist and iron chloride etching solution. In relief platesthe resist protects the image areas from the action of' the etchingfluid and in intaglio plates the resist protects the nonimageareas.Inbothcasestheresistisremoved after etching by suitable means to preparethe plate for printing. Some other practices are occasionally employed,varying in details and in -materials. All, however, are characterised inthat a colloidal material sensitised to light iscarrledbytheplateandisexpomtolightcorresponding to the image ornon-image areas. as thecasemaybe,inaccordancewiflrthesnbjectmattertobereproducedandthennhardenedareasorcoatingareremovedandtheplateis used for printing, eitherdirectlywlththehardened areas of coating remainingthereon. orby etchingthe plate and thereafter removing the hardened areas. In accordancewiththepresent features hereinafter fully described, and particularlypointed out in the claims, the following description setting forth indetail certainillustrative embodiments of the invention, these beingindicative however, of but a few of the various ways in which theprinciple of the invention may be employed.

In accordance with the invention, a solution for plate coating isprepared, of arabogalactan. A convenient and desirable solvent is water,arabogalactan being a known polysaccharid, and usually assigned theformula derived in one mode of manufacture from wood, and being in itscommercial state a dry, white, light-weight powder, and its molecularweight being around 2500, dissolving in water much more readily'thanalbumen or gum arabic, and

going into solution almost immediately whereas albumen or gum arabicusually requires soaking in water for several hours. It forms clearcolorless solutions which may be of very highconcen-' tration or asdesired. Such solutions have a notably lower viscosity than albumen orgum' in affording controllable uniformity in grade,

unlike the variations in such natural products as albumen and gumarabic.

The aqueous solution of arabogalactan of. desired concentration forcoating the plates is ap plied in suitable manner, and a lightsensitizing agent is provided, such as a chromate or bichromate, andmost conveniently this may be included in the solution before. coatingthe plates. Where desired, the plates may however be coated with the 1solution and dried, and

' the sensitizing agent may be applied subsequently, as for instance inalcoholic solution. The proportions of the ingredients are notcriticaland-ingeneralmaybesimilartothoseemployed in albumen and gumarabic solutions. However, and particularly where a thickercoatinvention, it now becomes possible to produce. ing is desired, theproportion of arabogalactan may be increased to any degree consistentwith the results desired. The plates or place to which the coating isapplied, may be of the customary character and metals, zinc, aluminum,etc.

As an example of the manufacture of ordinary lithographic plates, asolution comprising about per cent of arabogalactan and about 3 per centof ammonium bichromate in water, is applied to the plates, and thesensitized coating is allowed to dry. The plates are exposed to a lightimage in the usual way, and developing ink is then applied and theunexposed portions are removed with water, leaving the hardened exposedportions of the arabogalactan coating on the plate in ink-receptivecondition. The developed plate is then treated with a de-sensitizingsolution of usual or preferred composition for rendering thenon-printing areas ink-repellent and water-receptive. The plate may thenbe put on the press for printing. Such a plate comprises printing areasformed of arabogalactan hardened by light action.

As an example of the preparation of deep etched lithographic plates, awater solution comprising about 20 per cent of arabogalactan and about 6per cent of ammonium bichromate is coated onto the plates, and afterdrying, the plates are exposed to light corresponding to the non-imageareas of the subject. The unexposed coating is removed by dissolvingwith water, and the plate is etched with the usual iron chloride andlactic acid solution or other preferred solution, and lacquer'and inkare applied as usual. The hardened resist is then removed with dilutecitric acid solution, and the non-image areas are de-sensitized to ink,and used for printing.

As an example of the manufacture of copper half-tone relief or intaglioplates, a solution comprising about 10 per cent arabogalactan and about3 per cent ammonium bichromate is coated onto the plates and treatedsimilarly as in the example preceding. The etching action however, iscarried further to provide pronounced elevations or depressions and makeup the print-- ing surface.

Other modes of applying the principle of the the plate may then beinvention may be employed, change being made as regards the detailsdescribed, provided the features stated in any of the following claims,or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. As a light-sensitized material for photographic and printing purposesan aqueous solution of arabogalactan and a light-sensitizing agentcapable of acting thereon.

2. As a new article of manufacture, a plate for printing usage,comprising a metal supporting base portion and a surface thereonembodying arabogalactan and a light-sensitizing agent.

3. As a new article of manufacture, a plate for printing usage,comprising a metal supporting base portion and a surface thereonembodying arabogalactan and a light-sensitizing chromic acid compound.

4. As a new article of manufacture, a plate for printing usage,comprising a surface of arabogalactan and a light-sensitizing chromicacid compound.

5. As a new article of manufacture, a plate for printing usage,comprising'a base and a surface coating thereon of arabogalactan and alightsensitizing agent capable of acting on the arabogalactan.

6. As a light-sensitized material for photographic and printingpurposes,an aqueous solution 'of arabogalactan and a light-sensitizingchromicacid compound. 7

'7. As a new article of manufacture, a plate for printing usage,comprising a base and a surface coating on said base having areas forreproduction and embodying hardened arabogalactan resulting from theaction of a light-sensitizing agent capable of acting thereon andexposure to actinic rays.

. 8. As a new article of manufacture, a plate for printing usage,comprising a base and a surface coating on said base having areas forreproduction and embodying hardened arabogalactan resulting from theaction of a light-sensitizing chromic acid\compound and exposure toactinic rays.

WILLIAM H. WOOD.

